Are Online Roof Estimates Accurate?
"i had to pay extra as some of the decking had to be replaced that wasnt anticipated."
That is how one r/Roofing reply describes what happened on the writer's own job.
An online roof estimate is a first look from above, not a price to plan around. The calculator measures your roof from images, and images cannot show the decking, the wood boards under your shingles. A roofer who visits, looks and writes down what the work includes is what turns that figure into one you can rely on. Until then, treat the number on your screen as a starting point.
Quick answer:
- Use the online figure to decide whether to ask for a visit, not to set a budget.
- Ask each roofer who visits for a written quote that lists the work, the materials and the costs.
- Ask how extra work is approved before you sign anything.
- Keep the quotes side by side and compare them point by point.
The number on your screen does not commit you to anything today. What counts is what gets written down once someone has looked at your roof.
What can a view from above not show?
A picture taken from above cannot show the wood under the shingles, the attic side of the roof or damage that is hidden. Nobody on the ground or in the sky sees those from a screen.
Insurers use aerial images too, and the pattern is the same. In Connecticut, aerial imagery is often used as a screening tool and may be followed by a physical inspection1 if concerns arise. In Tennessee, the age and clarity of aerial photography must be considered2 before relying on it. A picture from above is where the checking starts, not where it ends.
Not sure what happens when a roofer visits to give you a quote? How to get a roof quote that lists the work.
Why can the number move once the roof is opened up?
Because the decking and the framing under it are part of the job, and a screen cannot show them. During a repair or replacement, the condition of the roof deck and framing must be documented3, and new roofing must not be installed on damaged structural roof components3. So if the wood is damaged, it gets dealt with before the new roofing goes on, and a figure that left it out is missing a piece.
Another reply in a roofing thread names the fear: "when it’s opened up and materials alone are going to exceed the estimate". You can't remove that risk by staring at the calculator. You can ask about it before anyone signs, and that is cheaper than finding out halfway through.
What to get in writing
A reply in r/homeowners puts the lesson in one line: "I think you should've either had your own estimate done, or made sure you heard from the estimator exactly what would be done."
Ask the contractor for a written explanation of the work, a list of materials, a timeline, a breakdown of the costs and the warranty details4. Use that as your checklist:
- The work, in plain words: what will be replaced and what will be left.
- The materials, by name.
- The timeline, with a start and a finish.
- A breakdown of the costs and the warranty details.
Then add one more line: how extra work is approved. A change order is a signed page that records any extra work. By signing it, both parties agree to the changes in scope, cost and schedule5. Ask whether your own contract has a step like that.
Ask the roofer to put the hidden-wood question in the quote too. You can send this:
Please write in your quote the price per sheet for replacing damaged decking, and how much hidden damage can add before you stop and get my signed change order. Please also send photos of any damaged wood you find.
If a roofer won't put this in writing, or pushes you to sign today, that is an answer too. Choose a licensed, bonded and insured professional with a local address, get multiple estimates and don't give in to high-pressure sales6.
Holding an online figure and a different number from a visit? How to compare roof estimates when the totals don't match.
Quick questions
How much is 100 square feet of roof?
It is one roofing square, a unit for measuring roof area equal to 100 square feet7. Ask each roofer to write the size they measured in squares, so the quotes line up.
What is the 25% rule for roofing?
It is a building-code rule. In Florida, the code limits repair, replacement or recovery to 25 percent of a roof or roof section in any 12-month period8 before the whole roofing system or section must meet the code. Wherever you live, ask the roofer and your local building department how it applies to your roof.
How do I work out what a new roof will cost?
A figure for your roof starts with its size and with what is under the shingles, and only someone on the roof can check the second. Ask for a breakdown of what the price includes and of what could change it once the old roofing is off.
Does my insurer judge my roof from the sky too?
It may. In Connecticut, insurers may inspect a roof in person, with satellite images or drone photography, or with both1. If a letter about your roof arrives, ask what it was based on and whether anyone will look at the roof in person.
Sources
1. Connecticut Insurance Department, Understanding How Insurers Evaluate Roof Risk - FAQs
3. IBHS, Roof Guide: Codes & Standards
4. North Carolina Department of Insurance, Avoiding predatory roofing scams
7. NRCA, Roofing Guidelines Glossary: Square
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